1. Field of the Invention
The present invention relates to electrophotographic photoconductors and electrophotographic apparatuses utilizing the electrophotographic photoconductor.
2. Description of Related Arts
In recent years many electrophotographic photoconductors are proposed and put to practical use, as photosensitive characteristics of organic electrophotographic photoconductors using organic photosensitive materials are free of pollution, less costly, and flexibility of designing electrophotographic characteristics provided by wide variety in material selection.
Photosensitive layers of organic electrophotographic photoconductors have been proposed, which mainly consist of layers dispersing organic photosensitive materials in resin. The photosensitive layers are, for example, laminated structures formed by laminating layers dispersing charge generating substances in resin (charge generating layers) and layers dispersing charge transfer substances in resin (charge transfer layers), and single layer structures formed of single layers dispersing charge generating substances and charge transfer substances in resin.
Particularly photoconductors using photosensitive layers of function separated type which charge transfer layers are laminated on charge generating layers are widely put to practical use, since they have good photoconductor characteristics and durability. These laminated photoconductors of function separated type are used in negative charging processes, since hole transfer substances are mainly used in the charge transfer layers utilized for the laminated photoconductors of function separated type. However, as negative polar corona discharge used in negative charging processes is less stable and generates more ozone than positive polar corona discharge, harmful effects to photoconductors and operation environments have been problems.
As organic electrophotographic photoconductors usable with positive charge are effective in solving these problems, positively charged photoconductors with high sensitivity are required. A great number of positively charged photoconductors have been proposed, which are function separated type photoconductors with a charge generating layer laminated on a hole transfer layer or an electron transfer layer laminated on a charge generating layer as photosensitive layers, or single layer type photoconductors which charge generating and charge transfer substances are contained in a single layer. However, many of them have fallen behind negatively charged function separated type photoconductors in electric properties such as sensitivity.
Therefore in recent years, many electron transfer substances and electrophotographic photoconductors using them have been proposed, published, and attracted attention, for example in Japanese Patent Application Laid-open No. 1989-206349; Japanese Patent Application Laid-open No. 1992-360148; The Society Journal of Electrophotography, 30, 266-273 (1991); Japanese Patent Application Laid-open No. 1991-290666; Japanese Patent Application Laid-open No. 1993-92936; Preprints for Pan-Pacific Imaging Conference/Japan Hardcopy '98 Jul. 15-17, 1998 at JA Hall, Tokyo, Japan, p. 207-210; Japanese Patent Application Laid-open No. 1997-151157; Collection of papers of Japan Hardcopy '97, Jul. 9, 10, and 11, 1997, JA Hall (Otemachi, Tokyo), p. 21-24; Japanese Patent Application Laid-open No. 1993-279582, Japanese Patent Application Laid-open No. 1995-179775; Collection of papers of Japan Hardcopy '92, Jul. 6, 7, and 8, 1992, JA Hall (Otemachi, Tokyo), p. 173-176; and Japanese Patent Application Laid-open No. 1998-73937. Further, photoconductors using single layer type photosensitive layers in combination of hole transfer substances and electron transfer substances such as described in Japanese Patent Application Laid-open No. 1993-150481; Japanese Patent Application Laid-open No. 1994-130688; Japanese Patent Application Laid-open No. 1997-281728; Japanese Patent Application Laid-open No. 1997-281729; and Japanese Patent Application Laid-open No. 1998-239874 attract attention because of high sensitivity, and some of them have been put to practical use.
In single layer type of electrophotographic photoconductors described above, however, though electric properties such as initial sensitivity and residual potential are good, there still remain problems such as change in electric properties due to repeated use. In a word, satisfactory products have not been obtained at present. While photoconductors containing hole transfer substances of the present invention have been described in Japanese Patent Application Laid-open No. 1996-211636. However, there is no description of photoconductors containing electron transfer substance in the Application.
Therefore, the purpose of the present invention is to provide electrophotographic photoconductors having single layer type photosensitive layer containing electron transfer substances and electrophotographic apparatuses comprising them. The electrophotographic photoconductors eliminate the drawbacks described above and, have good electric properties in positive charge and good stability in repeated use.